SEOUL, South Korea — At a time when dynastic rule is under attack in popular uprisings throughout the Middle East, the heir apparent to the North Korean dictator Kim Jong-il smoothly acceded to a senior position on the National Defense Commission, the country’s most powerful body, according to a report on Wednesday by a leading newspaper in Seoul.

The newspaper, the Chosun Ilbo, citing an unidentified source in North Korea, said that Mr. Kim’s youngest son, Kim Jong-un, had cemented his position as the second most powerful person in the country when he was named recently to the post of vice chairman of the defense commission, which is led by his father.

The move was announced at a mass gathering of military leaders and security officials on Feb. 10, according to the newspaper’s source, but emerged only Wednesday, as the 69th birthday festivities for the elder Mr. Kim were in full swing in the capital, Pyongyang.

The government may be saving up for 2012, the centennial of the birth of the country’s founder, Kim Il-sung, and the year the ailing Mr. Kim has heralded as a deadline for building a “powerful, prosperous” nation. Mr. Kim suffered a stroke in 2008 and is thought to have diabetes, kidney failure and cardiovascular problems.

The South Korean government marked his 69th birthday by sending “unification balloons” carrying 100,000 propaganda leaflets over the border, a South Korean Web site, the Daily NK, reported. At a ceremony before the launching, a lawmaker with the governing Grand National Party in South Korea, Lee Doo-ah, read a statement saying, “The succession from Kim Jong-il to Kim Jong-un is a violation of the universal and reasonable values of human beings and a tragic act against history.”

Just days before Mr. Kim’s birthday, his second son, Kim Jong-chol, 30, was in Singapore attending a concert by the legendary guitarist Eric Clapton, Agence France-Presse and other news outlets reported. Amateur video from the scene showed a young man bearing a strong family resemblance strolling through the venue trailed by men in civilian clothes who tried to shield him from the cameras. Apparently a dedicated fan, Kim Jong-chol attended a series of Clapton concerts in 2006, following the British star to performances in four German cities, A.F.P. reported.

Photo

Kim Jong-un, center, the youngest son of Kim Jong-il, was displayed on a big screen on Wednesday at a performance to celebrate his father's birthday.Credit
Kyodo/Reuters

The North’s official Korean Central News Agency also said that with the day’s festivities the country was “paying high tribute to the undying feats that General Secretary Kim Jong-il has performed by leading the cause of building a thriving nation to victory.”

South Korean government officials could not immediately confirm Kim Jong-un’s promotion, and the North Korean news agency had made no mention of it by Wednesday afternoon.

“Kim Jong-un assuming such a position is quite natural, and not surprising,” said Paik Hak-soon, director of the Center for North Korean Studies at the Sejong Institute near Seoul. “It’s not too early for something like this. Sooner or later it was to be expected.”

Although his emergence as a serious political figure has been undeniable, some political experts had remained unconvinced that Kim Jong-un was secure in his anointed position. But if the report of his promotion to the No. 2 post on the National Defense Commission is true, they said Wednesday, there can be no further doubts.

“He is in a very special and unique category, and nobody else can be included as possibly assuming the supreme leadership,” Mr. Paik said.

The 15-member defense commission has several vice chairmen, including Jang Song-taek, the leader’s brother-in-law and the younger Mr. Kim’s uncle. It is widely believed that Mr. Jang, the husband of Kim Jong-il’s sister, has effective day-to-day control of the country.

But in terms of power and position, “Kim Jong-un is already ahead of Jang Song-taek,” Mr. Paik said.

“Jang Song-taek is the most powerful and loyal guardian” for the heir apparent, he said. “But it’s not possible for him to be promoted to supreme leader.”

North Korea watchers in the South, lacking reliable and verifiable information about the North’s succession drama, were abuzz recently over television images showing the senior and junior Kims at an art show in Pyongyang: both men were wearing black pants, identical padded and oversize cargo coats and matching brown fur hats.

Correction: February 16, 2011

An earlier version of this article incorrectly transliterated the name of the second son of Kim Jong-il. He is Kim Jong-chol, not Kim Jong-choi.

Correction: February 16, 2011

An earlier version of this article also said that 100,000 balloons had been sent into North Korea from the South; in fact, it was 100,000 pamphlets carried by a small number of balloons.

A version of this article appears in print on February 17, 2011, on page A4 of the New York edition with the headline: Son of North Korean Leader Is Given No. 2 Post, Report Says. Order Reprints|Today's Paper|Subscribe